A subscriber line interface circuit typically utilizes differential mode signaling when communicating with subscriber equipment such as a telephone. Differential mode signaling offers a number of practical advantages. For example, individual signals for each of the tip and ring lines need only have half the amplitude of the differential signal.
In order for the differential signaling to function appropriately, the differential signaling device requires longitudinal balance for the differential mode circuitry. Asymmetries between the drivers for each line may impair the ability to reject common mode signals. In particular, common mode signals will leak into the differential mode signals thus degrading of the performance of the differential circuitry.
In order to improve the performance of the differential circuitry, the common mode feedback circuit may be designed as an adjustable component of the differential circuitry. The common mode feedback circuit is adjusted or calibrated to maximize rejection of the common mode component of any signal presented to a differential node pair of the differential circuitry.